Various access control mechanisms are known, including, but not limited to, single and segmented garage doors, pivoting and sliding doors and cross-arms, rolling shutters, and the like. In general, an operator system for controlling such movable barriers includes a primary barrier control mechanism coupled to a corresponding barrier and configured to cause the barrier to move (typically between closed and opened positions).
Some movable barrier operator systems are equipped with safety sensors for detecting obstructions in the path of the movable barrier's movement. Safety sensors generally function to prevent a moving gate from striking an object or a person and causing damage. Typically, when an obstruction is sensed, the operator would disallow the operation of the barrier. However, safety sensors are subject to misalignment and other operation failures. For example, when optical sensors, such as a photo-eye sensor, become misaligned, the sensors would indicate an obstruction to the operator when no obstruction is actually present. Detection of a false obstruction is common because many safety sensors in the interface electronics are designed to be failsafe. That is, a failure in the link of the sensor is detected by system to be the equivalent of an obstruction, and the operator responses to the failure of a sensor in a similar manner as an obstruction. When failure occurs, users are then prevented from gaining entrance through a movable barrier even though the barrier is safe to operate. Safety sensor failure is especially a problem for residential gates and garage doors in which the movable barrier may be the primary means of entrance into the residential premise.